Hermetic high frequency module and method for producing the same

ABSTRACT

The invention relates to a high frequency module with a hollow conductor structure, consisting of a housing bottom and a housing lid, preferably consisting of ceramic. The housing bottom and the housing lid are preferably co-ordinated with each other in terms their expansion characteristics. The adjusting device is mounted on the housing lid for positioning on the housing bottom, and consists of a raised photosensitive resist part which tapers conically starting from the housing lid. The adjusting device engages with the hollow conductor on assembly. The layer thickness of the adjusting device is approximately 100 to 200 um. The housing bottom and the housing lid are permanently interconnected by soldering, preferably using solders which are introduced galvanically in solder deposits. To this end, the solder is either applied locally to the housing lid surface or introduced in vias which are structured in the lid.

[0001] The invention relates to an arrangement according to the preamble of claim 1 as well as to a method according to the preamble of claim 9.

[0002] The millimeter-wave communication modules according to the invention operate, for example, in the GHz range and are used for the transmission of data in traffic engineering.

[0003] For producing metal-ceramic composite structures for waveguide uncouplings in millimeter-wave communication modules, the antenna substrates are soldered on waveguide throughfeeds in microwave housings with a hermetic closure. In the case of currently available manufacturing processes, so-called preforms are used for a hermetic closure which are inserted as intermediate layers between the ceramic cover and the housing. Important criteria for the quality of such connections are their stability with respect to changing temperatures and their reliability in the continuous operation. In addition, the exclusion of moisture from the housing interior plays an important role with respect to the electrical operation.

[0004] From International Patent Document WO 91/209699, a hermetic closure of ceramic-metallic housings for integrated circuits is known. In this case, ceramic housing covers are mounted and soldered by means of gold/tin preforms. The soldering process takes place at a temperature of below 400° C. by means of a heating electrode which is in contact with the housing, the cover and the housing being pressed on one another during the soldering operation.

[0005] A significant disadvantage of previous manufacturing processes is the low positioning tolerance when joining individual modules, which makes an automatic manufacturing more difficult or even impossible. The construction of waveguide uncouplings using preforms and the registration pins normally used for a precise positioning of the housing cover increases the time consumption and is acceptable only in the case of small piece numbers.

[0006] It is an object of the invention to provide a manufacturing process and an arrangement with increased positioning tolerances in the automated production of hermetic HF modules.

[0007] With respect to the arrangement, the invention is reflected by means of the characteristics of claim 1 and, with respect to the method, it is reflected by means of the characteristics of claim 9. The additional claims contain advantageous developments and further developments of the invention.

[0008] The invention contains a high-frequency module with a waveguide structure consisting of a housing bottom and a housing cover, preferably made of ceramics. The housing bottom and the cover are coordinated with one another in their expansion behavior. For example, the housing cover will consist of aluminum oxide and the housing bottom will consist of Mo30Cu. On the housing cover, the adjusting device is mounted for positioning on the housing bottom. In order to prevent corrosion, the metallic housing is modified by means of a nickel and gold layer.

[0009] The adjusting device consists of a photosensitive resist elevation which, starting from the cover surface of the housing, tapers conically. During the mounting, the adjusting device engages in the waveguide. The layer thickness of the adjusting device amounts to approximately 100 to 200 μm. The housing cover and the housing bottom are firmly connected with one another by means of solders. Solders are preferably used which are galvanically fed into solder depots. For this purpose, the solder is either applied locally to the housing cover surface, which is in contact with the housing bottom, or is fed into vias (via circuits? translator) structured in the cover.

[0010] The method of producing a high-frequency module contains the following steps:

[0011] The contact surface of the housing cover is structured with the housing bottom with a first photo resist mask for a galvanic metal deposition;

[0012] a gold/tin layer sequence of the solder depot is deposited;

[0013] the first photo resist mask is removed;

[0014] a second photo resist mask is structured as the adjusting device;

[0015] the tin surface is cleaned of oxide;

[0016] the housing cover is centered on the waveguide and fixed;

[0017] the housing cover is soldered to the housing bottom;

[0018] the resist of the adjusting device is removed in a wet-chemical manner.

[0019] The resist of the adjusting device is preferably removed in a wet-chemical manner by means of a heated potassium hydroxide solution.

[0020] A special advantage of the invention consists of the simplification in the case of a manual construction of waveguide throughfeeds and permits an automatic assembly of the modules for a manufacturing of larger piece numbers.

[0021] Another advantage consists of the cost-effective integration of the manufacturing steps in the manufacturing of thin-layer substrates. This represents a significant simplification of the assembling process.

[0022] In the following, the invention will be explained in detail by means of advantageous embodiments with reference to schematic drawings in the figures.

[0023]FIG. 1 is a view of a high-frequency module with a waveguide structure;

[0024]FIG. 2 is a top view of the adjusting device;

[0025]FIG. 3 is a view of the housing cover with the adjusting device and the solder depot.

[0026] An embodiment according to FIG. 1 illustrates a high-frequency module with a waveguide structure, consisting of a housing bottom 1 and a housing cover 3 made of ceramics, in the case of which an adjusting device 4 for the positioning in the waveguide on the housing bottom 1 is applied to the housing cover 3.

[0027] For the centering and fixing on the waveguide throughfeed, the adjusting device 4 consist of a photo sensitive resist elevation which tapers conically starting from the housing cover 3 (FIG. 2). During the mounting, the adjusting device 4 engages with the upper conical surface 43 in the waveguide 5; is guided along the lateral surface 42 to the base surface 41; and is centered with a low bearing force in the waveguide. The dimensioning of the base surface 41 is such that it is coordinated in a precisely fitting manner to the dimension of the waveguide. The layer thickness of the adjusting device 4 amounts to approximately 100 to 200 μm. For achieving such layer thicknesses, normally two or three coating films of a thickness of approximately 70 μm are applied above one another. By means of the exposure parameters during the photolithographic process, the edge steepness of the lateral surfaces 42 is adjusted. The housing cover and the housing bottom 1 are fixedly connected with one another by means of solders 2 which are galvanically fed locally into solder depots 21.

[0028] The method of producing a high-frequency module contains steps in which a use of a preform is eliminated. The contact surface of the housing cover 3 is structured with the housing bottom 1 by means of a first photo sensitive resist mask for a galvanic depositing of metal. The gold/tin layer sequence of the solder depot used for this purpose is deposited such that its respective thicknesses are approximately adapted to the proportions of the eutectic alloy. A layer thickness ratio of the Au:Sn layers of approximately 1.5:1 is preferably endeavored and the solder depots 21 are filled thereby (FIG. 3). The respective layer thicknesses are in the range of between 12 μm Au/8 μm Sn to 9 μm Au/6 μm Sn. After the filling of the solder depots 21, the first photo sensitive resist mask is removed again. A second photo sensitive resist mask is then structured as the adjusting device 4. The mask normally consists of a photolithographically structured coating film. The oxide surface of the tin is removed in a hydrogen vacuum reflow furnace at a temperature of approximately 300° C. and a process time of several minutes. In another process step, the housing cover 3 is centered on the waveguide 5 and fixed.

[0029] The housing cover 3 is firmly connected with the housing bottom 1 by means of a soldering without any fluxing agent, such as an AuSn soldering in a hydrogen atmosphere. The soldering process is also carried out in a hydrogen vacuum reflow furnace preferably while using the eutectic solder material of an approximate composition of 80% by volume Au and 20% by volume Sn. The melting point of the eutectic compound amounts to 280° C. The soldering process of the furnace operated in a reducing hydrogen atmosphere in connection with nitrogen as a protective gas is carried out at a temperature of approximately 320° C. for a duration of several minutes. The used gold and tin layer, which is deposited on the soldering side of the substrate in depots, and, in the course of the tempering process, results in a complete mixing of the Au/Sn layers while forming a homogeneous structure, replaces the otherwise used preforms.

[0030] The resist of the adjusting device 4 is removed in a wet-chemical manner preferably by means of a heated potassium hydroxide solution. For this purpose, the module is immersed for approximately 10 minutes in a 50% potassium hydroxide solution at a temperature of 70° C. 

1. High-frequency module having a waveguide structure, consisting of a housing bottom (1) and a housing cover (3), characterized in that an adjusting device (4) for the positioning on the housing bottom (1) is mounted on the housing cover (3).
 2. High-frequency module according to claim 1, characterized in that the adjusting device (4) consists of a photo sensitive resist elevation.
 3. High-frequency module according to one of claims 1 to 3, characterized in that the adjusting device (4) conically tapers starting from the housing cover (3).
 4. High-frequency module according to one of claims 1 to 3, characterized in that the housing cover (3) and the housing bottom (1) are fixedly connected with one another by means of solders (2).
 5. High-frequency module according to claim 4, characterized in that galvanic solders (2) are galvanically fed into solder depots.
 6. High-frequency module according to one of the preceding claims 1 to 5, characterized in that the housing cover (3) consists of ceramics.
 7. High-frequency module according to one of claims 1 to 6, characterized in that the adjusting device (4) engages in the waveguide (5).
 8. High-frequency module according to one of the preceding claims 1 to 7, characterized in that the layer thickness of the adjusting device (4) amounts to approximately 100 to 200 μm.
 9. Method of producing a high-frequency module, consisting of a housing cover (3) with solder depots (21) and a housing bottom (1), characterized in that the contact surface of the housing cover (3) is structured with the housing bottom (1) with a first photo resist mask for a galvanic metal deposition, in that a gold/tin layer sequence of the solder depot (21) is deposited, in that the first photo resist mask is removed, in that a second photo resist mask is structured as the adjusting device (4), in that the tin surface is cleaned of oxide, in that the housing cover (3) is centered on the waveguide (5) and fixed, in that the housing cover (3) is soldered to the housing bottom (1), in that the resist of the adjusting device (4) is removed in a wet-chemical manner.
 10. Method according to claim 9, characterized in that the resist of the adjusting device (4) is removed in a wet-chemical manner by means of a heated potassium hydroxide solution. 